His candor helped propel Carson into the political spotlight. Well-known and highly respected for his medical expertise, motivational words and charitable works, the neurosurgeon claimed he would speak plainly about his beliefs.

Carson, who recently made headlines for commentary on social and political issues, said in a Fox News appearance that marriage was between a man and a woman. He said the definition could not be changed by members of the gay community or by "people who believe in bestiality." He also compared same-sex marriage supporters to pedophiles.

Some students complained, and the comments also were condemned by the medical school dean.

Carson later apologized for his language and said there were better ways he could have made his point. In an email to medical school dean Paul Rothman, Carson mentioned the attention surrounding statements.

"I believe it would be in the best interests of the students for me to voluntarily withdraw as your commencement speaker this year. My presence is likely to distract from the true celebratory nature of the day," he said.

Members of the Johns Hopkins Health and Human Rights student group had already started a petition to remove him as a commencement speaker at the diploma ceremonies for the schools of medicine and education before he withdrew.

Others believe Carson would have been a powerful motivator.

"He's, like, so respectful in all these other ways that people should not get so worked up over this kind of small thing," Hopkins student Lucy Gao said.

"In my opinion, my own personal comments might differ from what Dr. Carson says, but I think he's still a great neuroscientist and neurosurgeon, and he should be given credit for that," Hopkins graduate student Jagpreet Nanda said.

"I think that people should look at the whole thing in order to see that he's much more than this. He has done a lot, and I look up to him, definitely," Hopkins graduate student Justin Jacob said.

Commencement is May 23. At this point, no one has been chosen to replace Carson.